Is Lactose Intolerance a Sign of Celiac Disease?

Common but Reversible

Glass of milk and toast with cheese
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Lactose intolerance — where your body reacts to lactose-containing milk products with digestive symptoms — is very common in people with celiac disease when they're first diagnosed. Fortunately, it often improves once you've followed the gluten-free diet for a while.

To understand this phenomenon (and how it may affect you as a lactose-intolerant celiac), it helps to have a little basic information about what lactose is and how your body digests it.

What Exactly Is Lactose?

Lactose is a type of sugar that is present in milk. It's actually a combination of two different sugar molecules: glucose and galactose. To digest lactose, your body needs to break it down into those two smaller sugar molecules, which then can be absorbed into your blood stream.

Your body uses an enzyme called lactase to do the work of breaking down lactose into glucose and galactose. If you don't have enough of this enzyme in your small intestine, you can't split apart the lactose molecules, which means they move whole into your large intestine — and that's where the problems start.

Once whole lactose molecules make it that far into your digestive tract, the bacteria that normally live in your large intestine start to feast on it. This results in the nasty symptoms of lactose intolerance: nausea, cramps, bloating, gas, and diarrhea that appear a half-hour to two hours after eating.

Only a very few people are born without the ability to make lactase (human milk contains lactose, so it's intended to be part of our very first food). However, as children grow up, many gradually lose their ability to digest lactose. This is a natural process largely driven by our genetics.

Lactose intolerance is most common in people whose genetic ancestors didn't consume many unfermented milk products (such as East Asians, West Africans, Arabs, Greeks and Italians).

Meanwhile, it affects fewer than 5 percent of people with Northern European ancestry.

How Does Lactose Intolerance Relate to Celiac Disease?

As it turns out, the enzyme lactase that your body needs to break down those lactose molecules is produced by the very tips of your intestinal villi, tiny fingerlike projections in your small intestine that help you absorb nutrients. It's possible to develop lactose intolerance because of an injury to those villi.

In celiac disease, that's exactly what happens: Your immune system mounts an attack on your intestinal villi, leading to a process called villous atrophy in which your villi are injured or destroyed. When you don't have properly functioning intestinal villi, you can't make lactase — and therefore, you can't digest lactose. 

Celiac disease is a common reason for people to suddenly become lactose-intolerant. In one study conducted in Italy, researchers looked at 54 people who suffered from bloating and diarrhea after eating lactose-containing foods, and found about one-quarter of them actually had celiac disease.

Coping With Lactose Intolerance

There are several medical tests that can diagnose lactose intolerance, including a blood test, a breath test, and a stool test. If you're showing symptoms of lactose intolerance, your doctor may recommend you complete one of these tests to diagnose the problem.

Many people with lactose intolerance can handle eating certain dairy foods — such as cheese or yogurt — but they can't eat others without getting symptoms. If that's the case for you, consider tailoring your diet to skip the foods you know cause problems.

In addition, you can take over-the-counter lactase supplements (Lactaid is the best-known brand) to prevent digestive symptoms in situations where you can't avoid (or don't want to avoid) consuming dairy products.

If you have lactose intolerance and you've just been diagnosed with celiac disease, you're likely to find that your tolerance for lactose-containing foods improves the longer you follow the gluten-free diet. 

In fact, some researchers recommend that patients who are lactose-intolerant when they are first diagnosed with celiac disease should be retested for the condition after they’ve been gluten-free for a year. The gluten-free diet may have helped improve their lactase production to the point where they no longer need to avoid dairy products.

Sources:

National Digestive Diseases Information Clearinghouse. Lactose Intolerance fact sheet. Accessed Jan. 31, 2016.

National Library of Medicine Genetics Home Reference. Lactose Intolerance fact sheet. Accessed Jan. 31, 2016.

Ojetti V et al. High prevalence of celiac disease in patients with lactose intolerance. Digestion. 2005; 71(2):106-10.

Ojetti V et al. Regression of lactose malabsorption in coeliac patients after receiving a gluten-free diet. Scandinavian Journal of Gastroenterology. 2007; 5:1-4.

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